1. Field of Invention
The present invention relates to an electro-optical device in which a difference in surface level in the connection terminal-formed region is minimized, to a method for fabricating the same, and to an electronic apparatus using the electro-optical device as a display unit.
2. Description of Related Art
In general, in an electro-optical device, for example, in a liquid crystal device which performs a predetermined display using a liquid crystal as an electro-optical material, the liquid crystal is sandwiched between a pair of substrates. As one of such a liquid crystal device, for example, an active matrix liquid crystal device, in which a pixel electrode is driven by a three terminal switching element, has the structure described below. That is, one substrate of a pair of substrates constituting such a liquid crystal device is provided with a plurality of scanning lines and a plurality of data lines intersecting with each other. At each intersection thereof, a three-terminal switching element, such as a TFT (Thin Film Transistor), and a pixel electrode are formed as a set, and peripheral circuits for driving the individual scanning lines and data lines are provided in the periphery of the region (display region) in which these pixel electrodes are formed. The other substrate is provided with a transparent counter electrode facing the pixel electrodes. Additionally, an alignment layer, which has been subjected to rubbing treatment so that the long axis directions of the liquid crystal molecules are continuously twisted, for example, by approximately 90 degrees, between the two substrates, is provided on the inner surface of each substrate. A polarizer corresponding to the alignment direction is provided on the outer surface of each substrate.
Herein, image signals are usually supplied via image signal lines, and are sampled to the individual data lines by sampling switches with appropriate timing. The switching element provided at the intersection between each scanning line and each data line is turned on when a scanning signal applied to the corresponding scanning line is at an active level, so that the image signal sampled to the corresponding data line is supplied to the pixel electrode. The counter electrode provided on the counter substrate is maintained at a predetermined electric potential.
In such a structure, when the scanning signal supplied to each scanning line and the sampling signal for controlling the sampling switch are supplied with appropriate timing by the peripheral circuits, an effective voltage corresponding to the image signal is applied, pixel by pixel, to a liquid crystal capacitor composed of the pixel electrode, the counter electrode, and the liquid crystal sandwiched between both electrodes.
At this stage, light passing between the pixel electrode and the counter electrode is optically rotated by approximately 90 degrees along the twist of the liquid crystal molecules if the voltage difference between both electrodes is zero. As the voltage difference is increased, since the liquid crystal molecules are inclined in the electric field direction, the optical activity thereof disappears. Therefore, for example, in a transmissive electro-optical device, when polarizers in which the polarization axes are orthogonal to each other corresponding to the rubbing directions are disposed on the incident side and on the back side of the device, if the voltage difference between both electrodes is zero, light is transmitted, while as the voltage difference between both electrodes is increased, light is blocked. Therefore, by controlling the voltage applied to the pixel electrode for each pixel, a predetermined display is enabled.
In the rubbing treatment, usually, by rotating a buffing cloth wound around a roller, the surface of an organic film, such as a polyimide, is rubbed in a predetermined direction (rubbing direction). By the rubbing treatment, it is believed that the polymer backbone of the organic film is drawn in the rubbing direction and the liquid crystal molecules are aligned in the drawing direction.
However, a difference in level of approximately 500 nm to 1,000 nm occurs in the underlying surface on which the alignment layer is formed, in particular, in the underlying surface of one substrate provided with pixel electrodes, switching elements, scanning lines, data lines, and peripheral circuits, due to the presence or absence of various types of wiring, various elements, and contact holes. Even if an alignment layer is formed on the underlying surface having such a difference in level, a difference in level also occurs in the surface of the alignment layer. Moreover, if such an alignment layer is subjected to rubbing treatment, since the tips of fibers implanted in the buffing cloth become disordered due to the difference in level, the surface of the substrate is rubbed nonuniformly. If a liquid crystal is filled and sealed between the substrates in which rubbing treatment has been performed nonuniformly, display unevenness occurs, presumably because the liquid crystal molecules are not aligned in a predetermined direction. Specifically, striped display unevenness may occur, resulting in a decrease in display quality.
Objects of the present invention are to at least provide an electro-optical device in which a difference in level in the surface of the substrate is minimized, and thus inconvenience in display resulting from nonuniform rubbing treatment is prevented, to provide a method for fabricating the same, and to provide an electronic apparatus using the same.
The present inventors had believed that the difference in level which degrades the display quality most is a difference in level caused by connection terminals for inputting various signals from external circuits and wiring extending from the connection terminals.
This will be described in more detail. Since pixel electrodes and switching elements connected thereto are provided corresponding to the individual intersections between scanning lines and data lines, the pitch of the array thereof depends on the pitch of the array of the scanning lines and data lines. Moreover, since peripheral circuits including sampling switches are provided corresponding to the scanning lines and the data lines, the pitch of the array of the elements constituting the peripheral circuits also depends on the pitch of the array of the scanning lines and data lines. Therefore, since display unevenness due to the differences in level of such elements and wiring occurs at the same pitch as that of the array of pixels or at an integral multiple thereof, these are believed to be not conspicuous in view of display.
In contrast, in view of decreasing the length of wiring extending from the connection terminals and in view of maintaining the symmetry of the overall device, the connection terminals are disposed close to the sampling switches and a data line drive circuit for driving the data lines, and are arrayed in the extending direction of the scanning lines (i.e., in a direction orthogonal to the extending direction of the data lines), and also in view of facilitating the connection to the exterior, the connection terminals are formed at a much larger pitch than that of the array of the scanning lines and data lines, i.e., are formed independently of the pitch of the array of scanning lines and data lines. Therefore, display unevenness due to the difference in level of the connection terminals and wiring leading to the connection terminals is believed to be highly conspicuous.
(1) Accordingly, in one exemplary aspect of the present invention, an electro-optical device includes a substrate composed of a plurality of layers, an insulating film formed on the outer surface of the substrate, connection terminals for inputting image signals formed at substantially the same level of the insulating film, and wiring connected to the connection terminals.
In such a structure, it is possible to minimize a difference in level between the surface of each connection terminal and the surface in the periphery thereof, and thus the tips of fibers implanted in a buffing cloth can be prevented from becoming disordered in rubbing treatment.
(2) In this aspect of the present invention, preferably, the electro-optical device further includes a recess for forming a region of each connection terminal provided in at least one of the layers constituting the substrate.
In such a structure, it is possible to minimize a difference in level between the surface of the connection terminal and the surface of the insulating film formed in the recess.
(3) In this aspect of the present invention, preferably, a conductive film constituting the connection terminal is provided in the recess for forming the region of the connection terminal.
In such a structure, even if a pattern for forming the conductive film deviates, since the recess can be used as a margin, the conductive film can be reliably formed in the region of the connection terminals.
(4) In this aspect of the present invention, preferably, a recess for forming the wiring, which is connected to the recess for forming the region of the connection terminals, is provided in at least one of the layers constituting the substrate in the region of the wiring at least on the connection terminal side.
In such a structure, a difference in level due to the wiring leading to the connection terminals can be minimized.
(5) In this aspect of the present invention, preferably, the insulating film formed on the outer surface of the substrate is formed in the region of the recess for forming the region of the connection terminals and in the region of the recess for forming the wiring.
In such a structure, a difference in level between the surface of the connection terminals and the surface of the insulating film as well as a difference in level of the wiring leading to the connection terminals can be minimized.
(6) In this aspect of the present invention, preferably, the connection terminals are composed of a multi-layered conductive film.
In such a structure, a lower conductive layer can be also used as a conductive layer in the pixel region and in the peripheral circuit, and an upper conductive layer can be formed using a material suitable for a connecting body to be connected to the connection terminal.
(7) In this aspect of the present invention, preferably, a film for adjusting height composed of at least one layer is formed in the region of the recess for forming the connection terminal.
In such a structure, it is possible to level the surface of the insulating film formed in the region of the recess by adjusting the depth of the recess and the thickness of the connection terminal.
(8) In this aspect of the present invention, preferably, the depth of the recess is substantially equal to the sum of the thickness of the connection terminal and the thickness of the film for adjusting the height.
In such a structure, since the surface of the conductive film of the connection terminal formed in the recess is substantially level with the reference level, the difference in level in the periphery of the connection terminal can be substantially eliminated.
(9) In this aspect of the present invention, preferably, the film for adjusting the height is at least one of wiring formed in a display region and wiring constituting a peripheral circuit.
In such a structure, the wiring formed in the display region and the wiring constituting the peripheral circuit are used in common, which is further advantageous to the process.
(10) Preferably, the depth of the recess is substantially equal to the thickness of the wiring.
In such a structure, the film for adjusting height is not required.
(11) In another exemplary aspect of the present invention, an electro-optical device includes a substrate composed of a plurality of layers, connection terminals for inputting image signals formed on the substrate, a recess provided in at least one of the layers constituting the substrate at least in a section of the region for forming wiring leading to each connection terminal, the wiring formed in the region corresponding to the recess, and an insulating film formed on the wiring.
In such a structure, the level of the surface of the wiring formed in the recess is lower than the level of the surface of the connection terminal (pad) by the depth of the recess. Therefore, since the difference in level between the insulating film formed on the wiring and the surface of the connection terminal is reduced, it is possible to prevent the tips of fibers implanted in the buffing cloth from becoming disordered during the rubbing treatment.
Additionally, the recess may be directly formed in the substrate or may be formed in a laminate on the substrate. As the wiring, a low-resistance metallic film, such as aluminum, is preferably used. In such a case, the wiring itself may be used as the pad, or a conductive film composed of a different material, such as ITO (Indium Tin Oxide) deposited on the wiring may be used as the pad.
(12) In this aspect of the present invention, preferably, the connection terminal is composed of a conductive film constituting the wiring, and the insulating film formed on the wiring exposes the connection terminal.
(13) In this aspect of the present invention, preferably, the surface of the connection terminal and the surface of the insulating film are substantially level with each other.
In such a structure, a difference in level of the wiring leading to the connection terminal can be substantially eliminated.
(14) In this aspect of the present invention, preferably, the recess is formed in the region surrounding the connection terminal, and the wiring is formed in the region surrounding the connection terminal.
In such a structure, the region of the connection terminal can be formed by the recess. Additionally, the adjacent connection terminals are not short-circuited.
(15) In this aspect of the present invention, preferably, the surface of the insulating film formed on the wiring and the surface of the insulating film adjacent to the region in which the wiring is formed are substantially level with each other.
In such a structure, the difference in level of the wiring can be substantially eliminated.
(16) In this aspect of the present invention, preferably, the wiring is composed of wiring formed in a display region.
In such a structure, since the wiring can be composed of the wiring formed in the display region, it is not necessary to increase the number of process steps.
(17) In this aspect of the present invention, preferably, the wiring is composed of wiring constituting a peripheral circuit formed in the periphery of a display region.
In such a structure, since the wiring can be composed of the wiring constituting the peripheral circuit, it is not necessary to increase the number of process steps.
(18) In this aspect of the present invention, preferably, the wiring is composed of wiring formed in a display region and wiring constituting a peripheral circuit formed in the periphery of the display region.
In such a structure, the wiring leading to the connection terminals, the wiring formed in the display region, and the wiring constituting the peripheral circuit are used in common, which is further advantageous to the process.
(19) In this aspect of the present invention, preferably, at least one film for adjusting height is formed in the region of the wiring.
In such a structure, it is possible to level the surface of the insulating film formed on the wiring by adjusting the depth of the recess and the thickness of the wiring.
(20) In this aspect of the present invention, preferably, the depth of the recess is substantially equal to the sum of the thickness of the wiring and the thickness of the film for adjusting height.
In such a structure, since the surface of the wiring formed corresponding to the recess is substantially level with the datum level, it is possible to substantially eliminate a difference in level of the wiring leading to the connection terminals.
(21) In this aspect of the present invention, preferably, the film for adjusting height is at least one of wiring formed in the display region and wiring constituting the peripheral circuit.
In such a structure, the wiring formed in the display region and the wiring constituting the peripheral circuit are used in common, which is further advantageous to the process.
(22) In this aspect of the present invention, preferably, the depth of the recess is substantially equal to the thickness of the wiring.
In such a structure, a film for adjusting height is not required.
(23) In another exemplary aspect of the present invention, an electro-optical device includes a substrate composed of a plurality of layers, a display region formed on the substrate, wiring arranged in the display region, peripheral circuits formed in the periphery of the display region and electrically connected to the wiring, connection terminals formed on the substrate, wiring for electrically connecting the peripheral circuits and the connection terminals to each other, a recess provided in at least one of the layers constituting the substrate at a section in which the peripheral circuits are formed, and an insulating film formed on the peripheral circuits.
In such a structure, since the upper surfaces of the peripheral circuits can be leveled with each other, it is possible to reduce display unevenness due to a difference in level on the peripheral circuits.
(24) In another exemplary aspect of the present invention, an electro-optical device includes a substrate composed of a plurality of layers, a display region formed on the substrate, wiring arranged in the display region, peripheral circuits formed in the periphery of the display region and electrically connected to the wiring, connection terminals formed on the substrate, wiring for electrically connecting the peripheral circuits and the connection terminals to each other, a recess provided in at least one of the layers constituting the substrate at a section in which the peripheral circuits are formed, a recess for forming the region of each connection terminal, and an insulating film formed in the regions of the recess for the peripheral circuits and the recess for forming the connection terminal so as to constitute an outer surface.
In such a structure, since the upper surface of the peripheral circuits and the periphery of the connection terminals can be leveled with each other, it is possible to reduce display unevenness due to the difference in level on the peripheral circuits and in the periphery of the connection terminals.
(25) In another exemplary aspect of the present invention, an electro-optical device includes a substrate composed of a plurality of layers, a display region formed on the substrate, wiring arranged in the display region, peripheral circuits formed in the periphery of the display region on the substrate and electrically connected to the wiring, connection terminals formed on the substrate, wiring for electrically connecting the peripheral circuits and the connection terminals to each other, a recess provided in at least one of the layers constituting the substrate at a section in which the wiring arranged in the display region is formed, a recess provided in at least one of the layers constituting the substrate at a section in which the peripheral circuits are formed, a recess for forming the region of each connection terminal, and an insulating film formed in the regions of the recess for the peripheral circuits and the recess for forming the region of the connection terminal so as to constitute an outer surface.
In such a structure, since the surface of the display region, the surface of the peripheral circuits, and the periphery of the connection terminals can be leveled with each other, it is possible to reduce display unevenness due to the difference in level on the display region, on the peripheral circuits, and in the periphery of the connection terminals.
(26) In another exemplary aspect of the present invention, an electro-optical device includes a substrate composed of a plurality of layers, a display region formed on the substrate, data lines arranged in the display region, a data line drive circuit formed along one side of the display region, connection terminals formed so as to face the one side of the display region with the data line drive circuit therebetween, signal lines electrically connected to the connection terminals for supplying image signals to the data lines, a recess provided in at least one of the layers constituting the substrate for forming the region of each connection terminal, and an insulating film constituting the outer surface of the substrate and exposing the connection terminals.
In such a structure, particularly, since the data line drive circuit and the periphery of the connection terminals can be leveled with each other, it is possible to reduce display unevenness due to the difference in level in the region thereof.
(27) In this aspect of the present invention, preferably, the electro-optical device further includes a recess provided in at least one of the layers constituting the substrate at least at a section in which the signal lines are formed in the region between the data line drive circuit and the connection terminals.
In such a structure, the difference in level at the section in which the signal lines are formed can be reduced.
(28) In this aspect of the present invention, preferably, the electro-optical device further includes a recess provided in at least one of the layers constituting the substrate at a section in which the data line drive circuit is formed.
In such a structure, it is possible to reduce display unevenness due to the difference in level of the data line drive circuit.
(29) In this aspect of the present invention, preferably, the electro-optical device further includes a sampling circuit provided between the one side of the display region and the data line drive circuit for controlling the supply of image signals to the data lines in the data line drive circuit.
(30) In this aspect of the present invention, preferably, a recess is provided in at least one of the layers constituting the substrate at a section in which the sampling circuit is formed.
In such a structure, it is possible to reduce display unevenness due to the difference in level of the sampling circuit.
(31) In this aspect of the present invention, preferably, an alignment layer is formed in the display region and the rubbing direction of the alignment layer is directed from the connection terminals to the display region.
In such a structure, by leveling the region between the data line drive circuit and the connection terminals which is formed independently of the pitch of the pixel array, it is possible to reduce the display unevenness which is relatively easily visible.
(32) In another exemplary aspect of the present invention, an electronic apparatus includes a light source for emitting light, an electro-optical device according to any one of the above-described exemplary aspects of the present invention in which light emitted from the light source is modulated in response to image information, and a projection unit for projecting the light modulated by the electro-optical device.
When an electro-optical device is used as a projection display device, even slight display unevenness is enlarged in a projected image so as to be visible. However, since the electronic apparatus of the present invention is provided with an electro-optical device in which the regions for forming the connection terminals and wiring leading to thereto are planarized, it is possible to achieve high display quality in which display unevenness due to a difference in level is prevented.
(33) In another exemplary aspect of the present invention, a method for fabricating an electro-optical device, in which a predetermined image is displayed in response to signals inputted through connection terminals provided on a substrate composed of a plurality of layers, includes a step of forming a recess in at least one of the layers constituting the substrate at a section in which wiring leading to each connection terminal is to be formed, a step of forming the wiring in a region corresponding to the recess, and a step of depositing an insulating film on the wiring.
In such a method, in a manner similar to that in the first aspect of the present invention, a difference in level between the surface of the connection terminals and the surface of the insulating film as well as a difference in level of the wiring leading to the connection terminals can be reduced.
(34) In this aspect of the present invention, preferably, the connection terminals are formed simultaneously with the step of forming the wiring, and the method further includes the step of exposing the connection terminals covered by the insulating film subsequent to the step of depositing the insulating film.
In such a method, the difference in level in the periphery of the connection terminal can be reduced by a relatively simple process, such as etching.
(35) In this aspect of the present invention, preferably, the step of exposing the connection terminals is a step of polishing the insulating film.
In such a method, by using the surface of a conductive film constituting the connection terminal as a stopper, it is possible to perform substantially complete planarization relatively easily.